Thermoplastic polymers have long been used in the preparation of brush bristles. Such bristles have been prepared in a wide variety of configurations, including both solid and hollow monofilaments, and are generally tapered from the butt end to the tip end of the bristle. These polymeric bristles have provided advantages over natural bristles such as hog hair in both cost and performance for the brushmaker and durability for the consumer.
The performance advantages of polymeric materials in water based paints have long been recognized because natural hog bristle becomes very limp as it absorbs water. However, for premium quality brushes, boar bristle brushes have been preferred by the professional painter in oil based paint varnishes and shellac. The advantage of hog bristle in these applications is felt to be the random discrete flags at the tip end of the bristle. These flags increase the ability of a brush to hold and release paint and provide a smooth surface. Tipping is another commercial bristle finishing operation in which individual bristles are ground down to a fine point. Tipping and flagging are used together, individually and alternately. The art of finishing synthetic tapered bristles varies among manufacturers. However, all are aimed at duplicating the painting performance of hog bristle brushes.
A variety of hollow synthetic bristles have been previously developed, such as those described in Payne et al., U.S. Pat. No. 4,279,053. However, hollow brush bristles flag very easily, so that the flagging operation is usually minimized or eliminated by the brush manufacturer. Moreover, hollow bristles have not been favored in the professional paintbrush segment because of durability and cleanability.